176 U.S. NATIONAL MUSEUM BULLETIN 227 



is a characteristic and relatively stable feature; and that it is found 

 in the least saline part of the available habitat. 



In estuaries where the worms a.re subject to wide salinity variations 

 semidiurnally, semimonthly and seasonally, it may withstand ranges 

 of salinities from over 257oo or more down to salinities below l7oo- In 

 British estuaries, it penetrates farther into waters of low salinity than 

 any other "marine" type and may penetrate into nearly fresh waters. 

 In stable waters of low salinity, as in the practically tideless Baltic 

 Sea, it is found subtidally in shallow waters and encounters over much 

 of the year a low but relatively stable salinity; here it appears to be 

 limited to a salinity as high as 47oo- 



Smith (1955c) made a comparative study of N. diversicolor from 

 representative parts of its geographical range, under 4 different types 

 of salinity: (1) That of relatively stable high salinity of marine- 

 dominated population in Scotland and southern England; (2) rela- 

 tively stable low salinity of Baltic population in Gulf of Finland; 

 (3) varying salinities or estuarine conditions in southern England; 

 and (4) intermediate salinities in Denmark. He carried out ecological 

 and physiological studies in several localities in respect to salinity 

 tolerance and found that N. diversicolor shows a uniform pattern of 

 constant level of coelomic chloride regulation relative to salinity of the 

 medium regardless of the salinity of its regional background and that 

 there are no physiological races in respect to salinity tolerance. 

 A^. diversicolor behaves as a typical adjustor in higher salinities but as a 

 regulator in lower sahnities. Having long survived under conditions 

 of practically complete oxygen lack, it has great powers of osmoregu- 

 lation; it also has a wide temperature tolerance. 



It is found on bottoms of mud, clay, coarse and fine muddy sand, 

 fine gravelly sand, peat, among the roots of marsh grass. It is found 

 in coarse sand of exposed beaches as well as in fine firm mud of pro- 

 tected shores. It forms fairly permanent burrows, which may be a 

 simple vertical U-shaped gallery or comphcated by the presence of ad- 

 ditional branches with openings to the surface. According to Smidt 

 (1951) and others, although it tolerates very different conditions of life, 

 it seems to show a certain preference for the upper part of the tidal 

 zone and for a soft bottom; it thrives best where the bottom is sheltered 

 against too heavy movements of the water. It feeds on algal frag- 

 ments, dead crustaceans or molluscs, etc., and swallows the surface 

 mud around the openings of the burrow. 



According to Boguchi (1954), it is an omnivorous animal, eating algae, 

 mud, and vegetable and animal detritus; cannibalism was frequently 

 observed. The worms pull out of their burrows and brouse on the 

 surface of the mud. Heri)in (1926) found that it feeds on Entero- 

 morpha, Porphyra, diatoms, Zostera, and, at certain seasons when the 



